Various means for searching for a desired image from an image database in which a plurality of image data are stored have been proposed. Search processing methods of this type are roughly classified into:                methods of linking nonimage information such as a keyword or image sensing date and time to image data and executing search on the basis of it, and        methods of executing search on the basis of a feature amount (information such as luminance/color difference information, image frequency, or histogram) of an image itself.        
In the latter methods, a method of presenting an image to an image database and searching for an image using the feature amount of the image as a search key is particularly called similar image search. It has an advantage that an intuitively understandable search interface can be provided to a user who has no special knowledge about image processing.
This similar image search is sometimes executed on the basis of, e.g., the user's memory or an image idea uniquely presented by the user. Such a method is particularly effective when the user has no image data serving as a search key. However, similar image search based on such a manually drawn image is difficult with the above-described user interface of similar image search.
The user is also forced to do a cumbersome operation of, e.g., selecting a candidate image by the above-described keyword search and executing similar image search using the image obtained by this method as a key image.
In addition, in executing similar image search by “manually” drawing an image that the user remembers and using this image as a key image, a problem arises due to the fact that the human memory is ambiguous. Especially, for “colors”, a person often remembers only characteristic colors, and also often remembers colors such as “red” close to primary colors.
For this reason, even when the colors (RGB) of a manually drawn image are directly used as image search keys, it is often difficult to search for an image desired by the user. That is, in executing search using a manually drawn image as an original image, the user interface of similar image search is hard to use or unusable.